Snowmobile and rear suspension for snowmobile

ABSTRACT

A snowmobile rear suspension is shown comprised of a linear force element (LFE) positioned outside the envelope of the snowmobile endless track. The LFE is attached at one end to the frame and at the other end to a bell crank. The bell crank is operatively connected to the slide rails, and carrier rollers extend from the bell crank. When the slide rails collapse in normal operation, the bell crank strokes the LFE, and the suspension is progressive throughout the range.

RELATED APPLICATIONS

The present application claims priority to U.S. provisional patentapplication Ser. No. 61/104,436 filed Oct. 10, 2008, and is acontinuation-in-part application of U.S. patent application Ser. No.11/623,879 filed Jan. 17, 2007; the subject matter of both applicationsbeing incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to suspension systems for snowmobiles, andmore particularly, the present invention relates to snowmobile rearsuspensions. In an illustrated embodiment, progressive rate rearsuspension architecture for snowmobiles is disclosed.

Performance characteristics of snowmobiles, including the comfort of theride, depend on a variety of systems and components, including thesnowmobile suspension. Typically, a snowmobile suspension includes twosystems, a front suspension system for a pair of skis and a rearsuspension system for the track.

The rear suspension of a snowmobile supports an endless track driven bythe snowmobile engine to propel the machine. The track is supportedbeneath a vehicle chassis by a suspension that is designed to provide acomfortable ride and to help absorb the shock of the snowmobile crossinguneven terrain. Most modern snowmobiles use a slide rail suspensionwhich incorporates a pair of slide rails along with several idler wheelsto support the track in its configuration. The slide rails are typicallysuspended beneath the chassis by a pair of suspension arms, with eacharm being attached at its upper end to the chassis of the snowmobile,and at its lower end to the slide rails. The mechanical linkage of theslide rails to the suspension arms and to the snowmobile chassistypically is provided by springs and at least one element acting along alinear path, such as a shock absorber, damper, air shock, shock andspring combination, or other linear force element (LFE). The springs areloaded to bias the slide rails downwardly away from the snowmobilechassis and the shock absorbers; dampers or LFEs provide damping forcesfor ride comfort.

There are presently two general types of snowmobile rear suspensions inall of the snowmobile industry: coupled and uncoupled. The term“coupled” is given to suspensions that have dependant kinematicsfront-to-rear and/or rear-to-front (relative to the rear suspension railbeam). That is, a suspension is coupled “front-to-rear” when the frontof the suspension is deflected vertically and the rear also movesvertically to some degree. A suspension is coupled “rear-to-front” whenthe rear of the suspension is deflected vertically and the front alsomoves vertically to some degree. A suspension is considered to becoupled “tighter” front-to-rear, or increased coupling bias to thefront, if a front deflection causes near the same rear deflection. Thesame is true if a suspension is coupled “tighter” rear-to-front, orincreased coupling bias to the rear: a rear deflection causes near thesame front deflection. An uncoupled rear suspension functionsindependently front-to-rear and rear-to-front. A deflection of the frontportion of the suspension causes little to no deflection of the rearportion and vice versa.

There are two main advantages to a coupled suspension. First, a coupledsuspension shares rate when coupled. There is a distinct rate associatedwith the front of the suspension and a separate distinct rate associatedwith the rear of the suspension; when a suspension “couples” it borrowsthe rate of both the front and rear of the suspension so the overallrate becomes higher than could have been achieved without coupling.Second, coupling is used to control weight transfer during acceleration.An uncoupled suspension will allow excessive chassis pitch due to theindependence of the suspension. Coupling stops this by limiting theangle of the slide rail and by increasing the rate of the suspension and“locking” the suspension geometry.

Typically the use of a coupled suspension, uncoupled suspension, and thedegree to which a suspension is coupled depends on the expected use.Coupled suspensions are mostly used on trail/performance snowmobileswhere large bumps and tight corners require increased rate andcontrollable weight transfer. Uncoupled suspensions are used on deepsnow/long track snowmobiles where weight transfer and traction are moreimportant.

There are many ways to create a coupled rear suspension. The simplestform of a rear suspension is a four-link suspension created by thechassis, two arms, and the slide rails all connected with rotationalpivots. This type of suspension yields only one degree of freedom. Theslide rail motion and suspension kinematics are predefined by the lengthof the 4 links and cannot be altered due to the location of the input(front, rear, or between). This is not desirable because the slide railwill not follow undulating terrain or allow any angle change relative tothe chassis due to acceleration. To fix this problem with a basicfour-link, one of the links is allowed to change length to some degree.The geometry of the four-link therefore changes relative to the locationof the input. A deflection of the front portion of the suspension yieldsone distinct four-link geometry and a deflection of the rear portion ofthe suspension yields different distinct four-link geometry. There isalways some degree of uncoupled behavior in a coupled suspension whenthe geometry is not locked front-to-rear or rear-to-front. It isimportant to note that most coupling is focused on rear-to-front to helpcontrol excessive weight transfer. The majority of differences in rearsuspension architecture are driven by accomplishing this same goal of a“sloppy” four-link in different ways.

FIG. 1 illustrates an example of a traditional rear suspension 10(illustratively a 2D model of the Polaris Fusion® snowmobile rearsuspension design) having slide rails 12, a front suspension arm 14 anda rear suspension arm 16. Front suspension arm 14 is coupled to theslide rails 12 by pivot connection 18. An opposite end of frontsuspension arm 14 is pivotably coupled to the chassis. Rear suspensionarm 16 is pivotably coupled to the slide rails 12 by pivot connection20. An opposite end of the rear suspension arm 16 is pivotably coupledto the chassis. Torsion springs are illustratively mounted between therear torque arm and slide rails 12. First and second linear forceelements (LFE) 22 and 24 are coupled between the first and secondsuspension arms 14 and 16, respectively and the slide rails 12 in aconventional manner.

FIG. 1 labels the following geometry of a four bar link which is similarin most snowmobile rear suspensions as illustrated by the linesdefining: A) Front Link, B) Rear Link, C) Rail Link, and D) ChassisLink. These links and their relative lengths govern the majority of rearsuspension kinematics.

The coupling bias behavior as described above is dependant on thisfour-link geometry and is important to rear suspension rate, impactharshness, and ride quality. For example, a perfectly symmetricfour-link (A=B and C=D, A parallel to B and C parallel to D) will yielda rail angle that is maintained at the same angle throughout travel. Inother words, the rail 12 does not rotate relative to the chassis as thesuspension is compressed. This type of movement is not desirable due tothe need to achieve traction on undulating terrain. As deviations tothis symmetric geometry are made, the rail angle will change throughoutsuspension travel.

As traditional suspensions are compressed, the front arm begins to“point” at the rear arm mount location. This is known as “overcentering”. FIGS. 2 and 3 illustrate this graphically, showing how linksA and C have become substantially a straight line.

A rear suspension that is coupled rear-to-front has the sameover-centering problems as discussed above for a front load situation,but to a larger degree. FIG. 4 illustrates this problem graphically whena rear load is applied as illustrated by arrow 27, showing how link Bhas crossed over link C. As mentioned above, over-centering drasticallyreduces effective suspension rate and damper velocities.

The problem lies in packaging a four link geometry that does not moveover-center during compression. Consider another common four-linksuspension, the SLA (Short-Long Arm) suspension. FIG. 5 illustrates acommon snowmobile SLA front suspension 30 with labels equivalent to FIG.1 for links A, B, C and D. Details of the SLA front suspension aredescribed in U.S. Pat. No. 6,942,050 which is incorporated herein byreference. This arrangement does not move over-center upon compressiondue the placement of chassis mount points of A and B at locations 17 and19, respectively, in FIG. 5. The vertical separation is a highpercentage of link D. Therefore, the first factor in eliminatingover-centering in rear suspensions is to place the rear armsignificantly higher than the front arm as outlined in the abovediscussion about coupling behavior.

Simply moving the rear point of a conventional suspension upward is notfeasible. The rear arm needs to become significantly shorter than thefront. Typical link ratios (NB) on conventional suspensions are between1 to 1.5. Ratios other than this are not feasible or do not package incurrent design envelopes. However, to accommodate a higher rear mount,A/B ratios need to increase to the range of about 1.6 to 2.0. Therefore,in an illustrated embodiment, A/B ratios are preferably 1.6 to 2.0 orgreater in coupled suspensions. FIG. 6 illustrates the difference in arear load case coupling angle between a conventional suspension labeledas “Prior Art” (illustratively the Polaris IQ 440 suspension) and theillustrated embodiment described below (labeled as “Improved RearSuspension Coupled” and “Improved Rear Suspension Uncoupled”).

FIG. 7 illustrates the difference in the coupling angle between aconventional suspension and the suspension of the present improvedsuspension invention described below. Conventional suspensions yield afront coupling angle that increases through travel. This means that asthe conventional suspension is compressed, the angle of the slide railincreases. This type of behavior is not ideal because as the rail angleincreases, rate and damper velocities decrease ultimately resulting in aregressive suspension. More desirable is a rail angle that decreases asthe suspension is compressed; thus, effectively making the suspensionrate progressive (the more regressive the rail angle, the moreprogressive the rate). However, an increasing coupling angle isdifficult to eliminate due to the packaging of a traditional snowmobilesuspension. In the illustrated embodiment of the present invention,unconventional packaging of the suspension components results in avertical difference between the front arm and rear arm chassis mounts ofpreferably 20% or more of the chassis link length (D) which results in adecreasing coupling angle.

Further examination of coupling behavior yields two constraintsnecessary to maintain reasonable component loads and basic function ofthe rail/ground interface. First, this angle should be positive. Inother words, when a load is applied to the front of the suspension asillustrated by arrow 25 in FIG. 3, the front portion of the slide rails12 moves more than the rear portion and vice versa for a load applied tothe rear of the suspension. Second, there should be no inflections, orchange in sign of the slope, in the curve of rail angle versus verticaldeflection, as shown in FIGS. 6 and 7. In other words, when a load isapplied to the front of the suspension, at no point should the rear ofthe suspension begin to move faster than the front and vice versa for aload applied to the rear of the suspension.

Because an uncoupled suspension does not form a distinct four-link, noover-centering can occur. No link ratio is then necessary for a rearload case in an uncoupled suspension. This is very beneficial, butexcessive vehicle pitch and lack of vertical rate usually make uncoupledsuspensions behave poorly for load carrying capacity and ride quality.Typically, for these suspensions a link ratio is then tuned only for thefront load case. The shock/spring ratio can be tuned to help counteractthe deficiencies of an uncoupled suspension. In this way, the rear armgeometry is tuned exclusively to maximize rear load case rate.Therefore, linkage arm length ratios are tuned for front coupling andrear rate in uncoupled suspensions.

As discussed above, the majority of snowmobile rear suspensionarchitectures utilize a combination of springs, dampers, or othersimilar linear force elements (LFE), all packaged within the envelope ofthe track. Regardless of how these elements are packaged, these designstypically use two methods to generate vertical rate: 1) the LFE islocated so that there is some vertical component reacted between thesuspension arm and rail beam, and 2) the LFE is connected to thesuspension arm such that a torque reaction is generated about the upperpivot. The inherent problem is that these designs lose rate near fulljounce due to the suspension mechanism components becoming generallyplaner. That is, all the suspension components fold down until they arelying relatively flat as the suspension components move at full jounce.This is due to the large vertical travel requirements of a snowmobilesuspension.

The result of the suspension components becoming planar is that the loadvector of the LFEs begins to point horizontally instead of vertically.This transfers load into the internal components of the suspension anddoes not react vertically to suspend the vehicle. Also, as thesuspension components become planar, the moment arm through which thesuspension reacts increases at a faster rate than can be controlled bythe shock/spring ratio, regardless of the type of linkage used toaccelerate the shock/spring.

With reference again to FIGS. 1 and 2, FIG. 1 shows a 2D representationof suspension 10 at full rebound. FIG. 2 shows suspension 10 at fulljounce. The front and rear LFEs 22, 24 become generally planar and laydown and point nearly horizontally in FIG. 2. The rear torque arms get“longer” measured from the upper pivot to lower pivot in the horizontaldirection. Even with a complicated linkage to help stroke the rear LFE24, a progressive rate cannot be maintained due to the two reasonslisted above. This is true for all conventional snowmobile rearsuspension systems.

Load at the slide rails and, more importantly, the bias between frontand rear load is directly related to coupling, especially for a frontload case. Consider the traditional suspension as illustrated in FIG. 1.The architecture is such that the front spring/damper 22 acts betweenthe front arm 14 and the slide rail 12, and both the torsion springs andrear damper 24 act between the rear arm 16 and the slide rail 12 nearthe front. Therefore, during a front load case, both springs and dampers22, 24 have a large effect on load and rate. The same is true of a rearload case. Attempting to tune the front LFE 22 will change the load/rateat the front and rear, and vice versa. Also if the coupling wereincreased, the rail angle decreases through travel and the rate willincrease. In order to tune the suspension rate, the front LFE 22, rearLFE 24 and torsion springs, and coupling angle all need to be adjusted.

To improve this system: 1) Front coupling can be used primarily tocontrol front load/rate, 2) Front preload is adjusted by a small LFEnear the front of the rail (has a very small affect on rate), and 3)rear preload and rate is determined by the rear arm only. To achievethis with actual architecture, the main rear LFE needs to react only atthe rear arm and with no other suspension components. Therefore reactingthe LFE on the chassis in the above discussion is important not only forprogressive rate, but also for load bias. When these three conditionsare true, rear coupling does not greatly influence rate. This isrealized because the front LFE is only used for preload so there isgenerally very little rate to “borrow” from the front of the rail duringa rear load case.

Progressive rate suspensions have not yet been achieved in snowmobilerear suspension designs because 1) the vertical component of the LFEbecomes very small as the LFEs become horizontal and planar with thesuspension during jounce, and 2) the rotational component of the LFEabout the arm pivot also cannot increase faster than the increase in armlength moment.

The state of snowmobile rear suspensions in the industry consistsentirely of falling rate, or regressive suspension designs. Even thoughthere is a large variety in the suspension architecture from onemanufacture to another, commercially available designs yield an overallsuspension stiffness that decreases as the suspension is compressedtoward full jounce. Some architectures yield discontinuities that maylocally spike the rate for a short time (such as an overload spring),but afterwards the rate continues to decrease. Because most designeffort is directed at optimizing a damper or spring motion ratio insteadof analyzing the entire suspension system there are currently noprogressive rate suspensions in the industry.

Now with regard to chassis construction, traditional snowmobile chassisstructures consist of elements common to each manufacturer, especiallyin the tunnel and rear suspension portion of the snowmobile. Typically,the rear suspension includes two suspension arms attached to the chassistunnel frame and a drive shaft mounted forward of the front arm to drivethe endless track.

This conventional suspension arrangement poses two problems. First,track tension through suspension travel relies on the relative placementof the suspension arms and wheels to the drive shaft. Suspension mountlocations are often determined not only by specific, desired suspensioncharacteristics, but also on track tension packaging. Problems areencountered from both an over and under tensioning track standpoint.Second, the front arm placement is limited to remain outside the drivesprocket diameter due to interference with drive train components. Thiscreates problems when attempting to change the weight transfer behaviorof the rear suspension, which is dominated by front arm mount location.

Achieving the mount points for desirable rate and kinematics is onlyhalf the challenge of snowmobile suspension design. Packaging a trackaround the suspension is the other. Traditional suspensions sacrificemore optimum suspension geometry to provide track tensioning andpackaging which can be extremely difficult to manage.

All of these problems are solved by mounting the front swing arm coaxialwith the drive shaft as discussed below. Because the front swing armrotates around the same axis as the track drive sprocket, track tensionis only influenced by the slide rail approach bend profile and a rearsuspension idler pulley. Also, the coaxial placement of the arm createsimproved weight transfer behavior of the rear suspension.

In order to generate necessary traction under acceleration, weighttransfer and pitch need to be considered. Suspension parameters aretuned to facilitate the shift of vehicle weight from the skis to thetrack. This shift in weight is imperative for snowmobile accelerationdue to slippery ground conditions. There are many parameters, but thetwo that dominate are front arm mount locations and carrier wheel.

Vehicle pitch is partially a result of this weight shift, but excessivepitch can result without increased traction. Packaging constraints, suchas track carrier wheels, within the design of the suspension may limitor increase the ability of the vehicle to pitch.

With this design, the improved suspension may eliminate the carrierwheel. This changes the load vector into the suspension from the trackdue to tractive forces between the track and ground. In the illustratedembodiment, the load vector from the track is more horizontal whichinduces less pitch and weight transfer than a traditional suspension. Toimprove this, the front arm is moved significantly forward to facilitateweight transfer. This point can move forward incrementally until itencounters the drive wheel inscribed circle. At this point, it can onlymove coaxial with the drive sprocket. The illustrated embodiment of thepresent invention utilizes a coaxial front arm mount as discussed hereinto facilitate weight transfer and pitch.

As for the frame assemblies, traditional snowmobiles utilize a longtunnel structure to which the driveshaft and rear suspension mountsbeneath. Above the tunnel typically sits a fuel tank and seat. This typeof structure is adequate because most spring/damper forces are reactedinternal to the suspension and between the front and rear arm mounts.Additional structure to the base tunnel is only required between thesemounts.

SUMMARY OF THE INVENTION

The embodiments disclosed herein provide a snowmobile suspension system,comprising a frame; slide rails for mounting endless track; at least onelinkage between the slide rails and frame, the linkage comprising apivot link, where the pivot link pivots in response to movement betweenthe slide rails and the frame; and at least one linear force element(LFE) positioned between the pivot link and the frame, whereby pivotalmovement of the pivot link strokes the LFE.

The at least one LFE may be positioned above the frame. The at least oneLFE may be substantially horizontal throughout its movement. The atleast one linkage may be positioned adjacent to a rear of the sliderails and defines a rear suspension system. The pivot link may becomprised of a bell crank, which connects to one end of the LFE. Thelinkage may be further comprised of a rear suspension frame operativelylinked to the slide rails and the bell crank. The rear suspension framemay be comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

In another embodiment, a snowmobile suspension system, comprises aframe; slide rails for mounting endless track; at least one linkagebetween the slide rails and frame; and at least one linear force element(LFE) positioned above the frame and operatively connected to the frameand to the at least one linkage.

The at least one linkage may be positioned adjacent to a rear of theslide rails and defines a rear suspension system. The linkage may becomprised of a bell crank, which connects to one end of the LFE. Thelinkage may be further comprised of a rear suspension frame operativelylinked to the slide rails and the bell crank. The rear suspension framemay be comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

In yet another embodiment, a snowmobile suspension system, comprises aframe; slide rails for mounting endless track; at least one linkagebetween the slide rails and frame; and at least one linear force element(LFE) positioned substantially horizontally, with one end attached tothe frame and one end connected to the at least one linkage.

The at least LFE may be positioned above the frame. The at least one LFEmay be substantially horizontal throughout its movement. The linkage maybe comprised of a pivot link which pivots in response to movementbetween the slide rails and the frame, and LFE is positioned between thepivot link and the frame, whereby pivotal movement of the pivot linkstrokes the LFE. The at least one linkage may be positioned adjacent toa rear of the slide rails and defines a rear suspension system. Thepivot link may be comprised of a bell crank, which connects to one endof the LFE. The linkage may be comprised of a rear suspension frameoperatively linked to the slide rails and the bell crank. The rearsuspension frame may be comprised of straddle links, which flank theendless track. The straddle links may be defined as A-shaped links,having plural attachments to the slide rails and a single upper pivotlink. The bell crank may be pyramidally shaped, with front cornersattached to the frame, rear corners operatively connected to the sliderails, and the apex attached to the LFE.

In another embodiment, a snowmobile suspension system, comprises aframe; slide rails coupled to the frame; endless track mounted to theslide rail; at least one linear force element (LFE) positioned outsideof the envelope defined by the endless track; a suspension assemblycoupling the slide rails to the frame; whereby one end of the LFE isattached to the frame and the opposite end is attached to the suspensionassembly, with the endless track passing through the suspensionassembly.

The at least LFE may be positioned above the frame. The at least one LFEmay be substantially horizontal throughout its movement. The suspensionassembly may be comprised of a pivot link which pivots in response tomovement between the slide rails and the frame, and LFE is positionedbetween the pivot link and the frame, whereby pivotal movement of thepivot link strokes the LFE. The pivot link may be comprised of a bellcrank, which connects to one end of the LFE. The suspension assembly maybe comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present snowmobile will now be discussed withreference to the drawings, where:

FIG. 1 shows a diagrammatical view of a conventional snowmobilesuspension system in full rebound;

FIG. 2 shows a diagrammatical view of a conventional snowmobilesuspension system in full jounce;

FIG. 3 shows the diagrammatical view of a conventional snowmobilesuspension system according to FIGS. 1 and 2, with a front load applied;

FIG. 4 shows the diagrammatical view of a conventional snowmobilesuspension system according to FIGS. 1 and 2, with a rear load applied

FIG. 5 shows a diagrammatical view of a conventional snowmobile frontsuspension system;

FIG. 6 shows a comparison curve of the prior art versus the improvedsuspend with a rear load;

FIG. 7 shows a comparison curve of the prior art versus the improvedsuspend with a front load;

FIG. 8 shows a diagrammatical perspective view of the suspension of thepresent invention;

FIG. 9 shows a diagrammatical plan view of the suspension of FIG. 8;

FIG. 10 shows a diagrammatical plan view of the suspension of thepresent invention at full rebound;

FIG. 11 shows a diagrammatical plan view of the suspension of thepresent invention at full jounce;

FIG. 12 shows a diagrammatical perspective view of an alternatesuspension;

FIG. 13 shows a diagrammatical plan view of the suspension of thepresent invention retro-fit on an existing suspension;

FIG. 14 shows a diagrammatical plan view of another suspension of thepresent invention retro-fit on an existing suspension;

FIG. 15 shows a perspective view of the suspension of the presentinvention applied to a tunnel and to slide rails;

FIG. 16 shows a perspective view of the suspension of FIG. 16, with thechassis and tunnel removed;

FIG. 17 shows a plan view of the FIG. 16 embodiment;

FIG. 18 shows an enlarged perspective view of FIG. 16, showing the frontsuspension mounts;

FIG. 19 shows an enlarged view of the connection of the front suspensionmounts of FIG. 18 to the slide rails;

FIG. 20 shows a partial sectional view of one driveshaft assembly;

FIG. 21 shows the driveshaft assembly of FIG. 20, partiallydisassembled;

FIG. 22 shows a partial sectional view of another possible driveshaftassembly;

FIG. 23 shows the driveshaft assembly of FIG. 22, partiallydisassembled;

FIG. 24 shows an enlarged perspective view of FIG. 16, showing the rearsuspension mounts to the slide rails;

FIG. 25 shows an enlarged perspective view showing the pivotal slidingcoupling connection of the rear suspension mounts to the slide rails;and

FIGS. 26 and 27 show an additional rear suspension embodiment of thepresent invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Features and advantages of the present invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription of illustrative embodiments exemplifying the best mode ofcarrying out the invention as presently perceived.

The embodiments disclosed below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings.

A progressive rear suspension is disclosed for a rear suspension systemof a snowmobile. A progressive suspension is one having a stiffness thatincreases throughout (or at least substantially throughout) the entirerange of suspension travel.

A diagrammatical depiction of the progressive suspension is shown inFIGS. 8-14, and will be described representatively. This progressivesuspension provides improved ride with less bottoming and better energydissipation.

With reference first to FIGS. 8 and 9, an illustrated embodiment of asuspension 30 of the present invention is shown. Suspension 30 includesa pair of slide rails 12, and a swing arm 31 having a first end coupledto slide rails 12 at location 33 and a second end 35 pivotably coupledto the chassis. A frame 41 (FIG. 9) is configured to define a tunnel 40which receives the track 39 therein. In the illustrated embodiment, themain LFE 32 is located generally horizontally above the tunnel 40 withone end connected to the chassis at location 34 and the other end 36connected to a bell crank 38 that redirects the load vertically. Asecond LFE 37 includes a first end 43 which is pivotably coupled to theslide rails 12. A second end 45 of LFE 37 is pivotably coupled to link47. As shown in FIG. 8, an opposite end of link 47 is pivotably coupledto swing arm 31 by connector 49. As discussed below bell crank 38generally forms a triangular shape with corner 50 coupled to thechassis, corner 52 coupled to end 36 of LFE 32, and corner 54 coupled toend 45 of LFE 37.

It is understood that the actual architecture of the rest of thesuspension 30 may vary from what is shown in FIGS. 8 and 9. Many priorart suspensions may also benefit from this design by connecting thehorizontal LFE 32 to any of the suspension arms through a bell crank 38.The bell crank 32 redirects the shock load vertically. By changing thelength and angles between the input and output arms of the bell crank38, a progressive rate can be achieved for virtually any suspensiondesign.

As discussed above, the main LFE 32 is illustratively placed outside theenvelope defined by track 39 and above the tunnel 40 as shown in FIG. 9.One end 34 of the LFE 32 is connected to the chassis and the other end36 is connected to an end of a bell crank 38. The other end of the bellcrank 38 is connected to the suspension components, either through alink, pivot, slider, or other suitable connection. The suspensioncomponents extend around the track 39 in order to connect componentslocated within the envelope of the track 39 to the LFE 32. Details of anillustrated embodiment of this connection are described below.

As shown in FIG. 9, one such improved suspension places at least one LFEoutside the envelope defined by the track and above the chassis tunnel.One end of the LFE is connected to the chassis and the other end isconnected to an end of a bell crank. The other end of the bell crank isconnected to the suspension components, either through a link, pivot,slider, or other suitable connection. As the suspension compresses intojounce, the suspension end of the bell crank moves vertically someamount which causes the crank to rotate. This, in turn, causes the LFEend of the bell crank to move horizontally and stroke the LFE. This iswhat provides the vertical suspension rate.

Comparing an example of the improved suspension at full rebound (FIG.10) to full jounce (FIG. 11), it is shown that the horizontal distancefrom the crank pivot to the crank suspension end increases. Thisincrease of the “output” bell crank moment arm by itself would make thevertical load decrease through travel. However, the vertical distancebetween the crank pivot and the crank LFE end increases. This increasein the “input” bell crank moment arm balances the increase in the“output” and maintains the vertical load. By changing the relativelength of the arms and the angles between them, a progressive rate canbe generated for most suspension load cases.

The arm lengths and angles of the bell crank 38 are important to theoperation of the suspension 30. FIGS. 10 and 11 show the illustratedembodiment at full rebound and at full jounce, respectively. The largetriangle represents the bell crank 38. The left corner of the triangle50 below the LFE 32 is the pivot connector to the chassis. The top mostcorner 52 is connected to the LFE 32, and the bottom most corner 54 isconnected to the suspension (in this case through the link 47).Comparing the suspension 30 at full rebound (FIG. 10) to full jounce(FIG. 11), it is shown that the horizontal distance from the crank pivotto the crank suspension end increases. This increase of the “output”bell crank moment arm by itself would make the vertical load decreasethrough travel. However, the vertical distance between the crank pivotand the crank LFE end increases. This increase in the “input” bell crankmoment arm balances the increase in the “output” and maintains thevertical load. By changing the relative length of the arms and theangles between them, a progressive rate can be generated for mostsuspension load cases.

Another illustrated embodiment uses two bell cranks 42, 44 which connectto the suspension at two points so an LFE 46 is actuated from both endsas shown in FIG. 12. In this illustrated embodiment, the LFE 46 may beplaced front-to-back or left-to-right above the tunnel 40. FIG. 12 showsa design with the LFE 46 placed left-to-right between bell cranks 42,44.

As stated above, the present invention may also be applied to existingrear suspensions, and FIGS. 13 and 14 show a retro-fit to the PolarisFusion® rear suspension shown in FIGS. 1-3. FIG. 13 discloses use of asingle bell crank 38 coupled between rear suspension arm 16 and LFE 32.FIG. 14 discloses use of dual bell cranks 38 and 38′. In FIG. 14, afirst end of bell crank 38 is coupled to end 36 of LFE 32 and a secondend of bell crank 38 is coupled to rear suspension arm 16 by link 51. Asecond bell crank 38′ has a first end coupled to end 34 of LFE 32 and asecond end coupled to front suspension arm 14 by link 51′.

Operation of only one illustrated suspension architecture will bediscussed since the general operation is the same regardless of wherethe suspension end of the bell crank 38 is connected. As the suspensioncompresses into jounce, the suspension end of the bell crank 38 movesvertically some amount which causes the crank 38 to rotate. This, inturn, causes the LFE end of the bell crank 38 to move horizontally andstroke the LFE. This is what provides the vertical suspension rate.

With reference now to FIGS. 15-25, a complete depiction of oneembodiment of the rear suspension 60 of the present invention will bedescribed. Those elements referenced by reference numbers identical tothe numbers above perform the same or similar function.

With reference first to FIG. 15-17, rear suspension 60 is shown attachedto tunnel 40, and illustrates the suspension 60 coupled to a frame 41which defines the tunnel 40 for track 39 (FIGS. 16-17). This system isgenerally comprised of, slide rails 12, LFE 32, bell crank 38, tunnel40, chassis 70, front swing arms 80 and an A-shaped pivot member 96.More particularly, LFE 32 is shown suspended between bell crank 38 and achassis structure 70. Bell crank 38 is attached to A-shaped pivot member96, which in turn is attached to slide rails 12. FIG. 17 shows that themain LFE 32 is located horizontally above the frame 41 which defines thetunnel 40.

In the embodiment of FIGS. 15-17, and as best shown in FIGS. 16 and 17,a front swing arm 80 is pivotably coupled to the slide rails 12 by apivot connection 82 as discussed in further detail below. An oppositeend 84 of swing arm 80 is pivotably coupled to the chassis about which adrive mechanism 85 is attached, having an axis which is coaxial with adrive shaft 86 as also discussed in detail below. With reference firstto FIGS. 18 and 19, the connection of the front swing arm 80 to sliderail 12 will be described.

Traditional suspensions typically mount the front and rear control armsto the slide rails in one of two methods: 1) Pivot shaft extends betweenbeams and passes through a pivot tube on the arm, or 2) A left and rightpivot shaft is mounted to the beams and each pass through a small pivottube on the arm. Although both designs are relatively simple and haveworked well in current designs, there are several problems with both.

The long pivot shaft works well to distribute suspension loads across alarge area on the pivot shaft. However, maintaining lubrication isdifficult and high bending loads can be present thus requiring a largethrough fastener. The short left/right pivot design can be used withsmall self lubricated bushings, but the cantilevered load also requiresa large fastener.

A clevis joint design as shown in FIG. 19 solves the deficiencies ofeach of the above designs. The size of the joint makes it possible touse small lubricated bushings and because the clevis “straddles” therail beam, no bending load is present in the fastener so smallerfasteners may be used with equivalent durability. In this design, theclevis portion of the joint is part of the control arm.

Clevis connection 82 is provided between the swing arm 80 suspensioncomponents and slide rail 12 as shown in FIG. 19. Ends 112 of swing arm80 each include a slot 114 which receives a portion 116 of slide rails12 therein. Bolts 118 then secure the ends 112 to portions 116 of theslide rails 12.

With respect again to FIG. 18, the front drive mechanism 85 will bedescribed in greater detail. Drive shaft 86 rotates a plurality of drivesprockets 88 which have a plurality of teeth to engage and move thetrack 39 in a conventional manner. A pre-load spring 90 has a first end92 pivotably coupled to swing arm 80 and a second end 93 pivotablycoupled to slide rails 12 at pivot connection 94.

As mentioned above, conventional suspension arrangements pose twoproblems. First, track tension through suspension travel relies on therelative placement of the suspension arms and wheels to the drive shaft.Suspension mount locations are often determined not only by specific,desired suspension characteristics, but on track tension packaging.Problems are encountered from both an over and under tensioning trackstandpoint. Second, the front arm placement is limited to remain outsidethe drive sprocket diameter due to interference with drive traincomponents. This creates problems when attempting to change the weighttransfer behavior of the rear suspension, which is dominated by frontarm mount location.

Both of these problems are solved by mounting the front swing arm 80coaxial with the drive shaft 86 as discussed above and shown in detailin FIG. 18. Because the front swing arm 80 rotates around the same axisas the track drive sprocket 88, track tension is only influenced by theslide rail 12 approach bend profile and the rear suspension idler pulley108. Also, the coaxial placement of the arm 80 creates improved weighttransfer behavior of the rear suspension 60.

There are two illustrated arrangements in which the arm 80 is mountedcoaxial to the drive shaft 86 either on the drive shaft 86 or thechassis. FIG. 18 shows the first arrangement where the arm 80 is mounteddirectly to the drive shaft 86. In this arrangement, bearings are usedin the connection to allow the drive shaft 86 to rotate within the ends84 of the suspension arm 80. The advantages of this connection aretwofold, lateral packaging of the arm 80 in the chassis tunnel iseasier, and the arm strengthens the drive shaft 86. In this embodiment,however, high speed bearings are required at this connection, and thedrive shaft 86 must now react to suspension loads.

The second arrangement for mounting the swing arm 80 is to use largerhollow connections between the suspension arm and the chassis. The driveshaft 86 then passes through this connection. In the illustratedembodiment, a quick change drive shaft assembly is designed to be easilyremoved from a chassis. This provides improved serviceability andmaintenance, and improved assembly procedure.

Traditional snowmobiles have typically used drive shafts that are widerthan the tunnel. This is to simplify the number of parts in the assemblyand still allow mounting to each edge of the tunnel with a single shaft.However, this makes assembly and service difficult. In order to removethe drive shaft you need to open the chain case, loosen the drive shaftbolt, slide the drive shaft out of the chain case, twist the drive shaftand remove it from the tunnel. Sliding the drive shaft and twisting tothe side can be very difficult due to the tunnel/track clearance.

The illustrated embodiment provides two designs that make this processeasier. The first design consists of a two part drive shaft assembly: aninner shaft and outer sleeve. The second consists of a removable splinestub that couples the shaft to the chain case.

This first sleeve embodiment is depicted in FIGS. 20 and 21, andincludes a drive shaft similar to current designs, but the drivesprockets 88 are mounted to an outer sleeve 180 (instead of the shaftdirectly) that is slightly narrower than the tunnel 40. The two partsare then torsionally coupled through either sliding splines, hexes, orother similar fit. The inner shaft 182 is tightly mounted to the chaincase 184 by means of a fastener and the outer sleeve 180 is compressedwhen the inner shaft 182 is tightened from the end opposite the chaincase 184.

To assemble this design, and as best shown in FIG. 21, the sleeve 180 isplaced in the tunnel and the shaft 182 slides completely through thesleeve 180, from the outside of the tunnel, into the chain case 184. Theshaft 182 is torsionally coupled to the drive mechanism inside the chaincase and fastened solidly with a screw 186. The chain case 184 has anaccess opening 187 to install the screw 186 so the case 184 does notneed to be opened to access the drive shaft 182. The entire assembly isclamped tight from the side opposite the chain case 184. As this istightened, the outer sleeve 180 is compressed from each end by the maindrive shaft bearings.

Alternatively, a drive shaft according to FIGS. 22 and 23 could be used,where a spline stub for coupling to the chain case 184 is female insteadof male. This allows the overall length of the shaft 188 and the amountof shaft protruding inside the chain case 184 to be small. A spline stub190 then torsionally couples the shaft 188 to the chain case drivemechanism 192.

To assemble this design, and with reference to FIG. 23, the drive shaft188 is positioned slightly off center from the tunnel, enough for thechain case end of the shaft to clear the tunnel wall. A notch is presentin the tunnel wall for the free end (non-chain case end) of the shaft topass through into the correct position. The drive shaft 188 is thenmoved toward the chain case 184 and pilots on the case bearing. Thespline stub 190 is then inserted from the outside of the chain case 184and torsionally couples the drive shaft 188 to the chain case drivemechanism 192. An access hole 187 is present in the case cover so thecase does not need to be opened to install or remove the stub 190. Afastener 191 is then threadably received in the end of the shaft 188,closest to the case 184, clamping the drive shaft 188 to the chain case.This fastener 191 is then enclosed by a cover 194 for the access hole187. Lastly, the free end of the shaft 188 is tightened against the maindrive shaft bearing.

Both methods are very beneficial with the coaxial mount suspension arm(discussed above). This allows the track and drive shaft to be assembledto the suspension and the entire suspension/track assembly placed intothe chassis all at once.

An important consideration in rear suspension design is maintainingtrack tension through suspension travel. If the track becomes loose, itwill skip drive sprocket teeth and damage the track. Extremely loosetracks can derail. Excessively tight tracks will yield high stresses oncomponents and cause track vibration, stretch, and damage.

Achieving the mount points for desirable rate and kinematics is onlyhalf the challenge of snowmobile suspension design. Packaging a trackaround the suspension is the other. Traditional suspensions sacrificemore optimum suspension geometry to provide track tensioning andpackaging which can be extremely difficult to manage.

The suspension of the present invention packages the suspension aroundthe track. That is, the track actually passes through one or moresuspension components. This design yields superb track tension valuesthroughout travel. Due to a lack of a carrier (upper) track wheel, andcoaxial mounting of the swing arm and drive sprocket, the tension in theillustrated embodiments only relies on the drive sprocket wheel 88 andidler wheels 108 to keep the track tight to prevent “unwrapping” aroundthe rail bend profile as shown in FIGS. 15-17. Track tension is easilytuned by sizing the idler wheel 108 with the drive wheel 88. Therefore,elimination of carrier wheel in conjunction with coaxial swing armmounting greatly simplifies track tensioning in the illustratedembodiments.

With respect now to FIG. 24, A-shaped rear pivot 96 will be described ingreater detail. As mentioned above, A-shaped rear pivot 96 connects bellcrank 38 to LFE 32. A-shaped rear pivot 96 is shown pivotably coupled tobell crank 38 by connection 98. A first arm 100 of pivot 96 is pivotablycoupled to slide rails 12 at location 102. As shown best in FIG. 25,second arm 104 of pivot 96 is coupled to slide rails 12 by a couplingslider 106, having an arced slot 107 that facilitates coupling betweenthe front and rear. A block 105 coupled to arm 104 moves back and forthin slot 107.

This improved suspension also uses a changing “rail link” length tofacilitate coupling. However, the pivot is considerably longer thantraditional due to packaging around and outside the track envelope sothat simple bumpers on the slide rail would not work effectively.Instead, the pivot is shaped as a triangle and the relative anglebetween the pivot and slide rails is limited by a curved slidermechanism, as described with reference to FIG. 25.

The advantages of this system are threefold. First, the horizontallength between the pivot-to-rail mount and the slider can be adjusted toreduce or increase the load within the slider system. Second, the loadbetween these two points is shared by the slide rail itself so noadditional structure is required on the pivot. Third, slots in theslider system provide lateral stiffness to the slide rails so additionalcomponents are not required to increase lateral strength or stiffness.

The following outlines the function of each component in the embodimentshown in FIGS. 15-17. The swing arm 80 is pivotally connected to thechassis coaxial with the drive shaft 86, low and forward on the sliderail 12 to facilitate weight transfer. The pivot 96 is pivotallyconnected to the slide rail 12 near the rear, and to an arced slot 107that facilitates coupling. The pivot 96 is “locked” to the slide rail 12at the extents of the slot 107. The geometry is coupled to the frontwhen the pivot is at the bottom, to the rear when the pivot is at thetop. The crank 38 is pivotally connected to the pivot 96 at one end 54and the chassis at the other end 50. The crank 38 acts as the rear armof the four-link. The preload spring 90 is connected between the swingarm 80 and the slide rail 12. This spring 90 is used for preload biasand does not appreciably affect rate. The main spring/damper 32 isconnected between the crank 38 and the chassis. The location on bothdetermines how progressive the suspension is.

As snowmobiles develop, accommodations in the chassis must be made forfaster, more powerful engines, longer travel suspension, more precisionhandling, and improved durability. This means the chassis must bestronger and stiffer. The most intuitive method to increase strength andstiffness is to directly connect the suspension hard points with moresignificant structure than a thin walled tunnel can provide. The resultis a direct load path between the front suspension mounts, the riderinput points, and the rear suspension mount points, such that the loadpath can only terminate in a structurally durable member of the chassis.

The chassis structure, especially in the rear section of the snowmobile,becomes considerably more important when the LFE reacts outside thesuspension, as described in the above discussion. In this case, rearsuspension loads are not only internal to the suspension, but aredirected into the chassis such that the chassis structure is an integralpart of the suspension. As discussed above, a suspension system isdescribed for support for the LFE 32 above the tunnel 40. The sub frame70 was shown in FIG. 15 for mounting LFE 32 above tunnel 40.

With reference now to FIGS. 26 and 27, a further embodiment will bedescribed. This embodiment shows a snowmobile rear suspension having abell crank 238, where bell crank 238 is connected to tunnel 40 at afront end 250 and to a pivot link 296 at 298, in a similar manner aspreviously described with respect to FIG. 15.

In addition, snowmobile suspension includes a carrier assembly 210having frame arms 212, 214 which suspend carrier rollers 216. Track 39would wrap around carrier rollers 216, around a drive roller 88 (FIGS.16, 17), around rail beams 12, and around idler rollers 108.

In this embodiment, the angle of the track 39 is increased from theangle of the track as depicted in FIG. 17, without carrier assembly 210.The tension of the track 39, in the embodiment of FIGS. 26-27, has avertical and horizontal component, with an increased vertical component,over the embodiment of FIG. 17. The vertical component is reactive inthe direction of the suspension. The carrier assembly 210, and the angleof the track (Ø), allows modification of the tractive force, and thestress on the rail beams 12, versus the vertical force. An increase tothe angle Ø, decreases the stiffness of the suspension, and makes thesuspension more supple. In the embodiment of FIGS. 26-27, Ø isapproximately 24°.

In some suspension designs, the rail beams have plastic sliders. Whenthe suspension jounces, the track can hit the sliders. This designprevents the track from hitting any part of the rail beams.

In summary, the embodiment of FIGS. 26 and 27 reduces the so-callednoise, vibration and harshness (NVH) by keeping the track off of anyplastic sliders on the rail beams. This design also reduces the loadinto the rail beams by reducing the horizontal component of the trackvector as mentioned above. Finally, this design reduces rear railstiffness by adding a larger vertical component of the track vector onthe idler.

Finally, while the bell crank 238 provides a convenient location for themounting of the carrier rollers, the carrier rollers could be mountedwithin the tunnel 40, and utilize the bell crank as shown in FIGS.15-17.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

1. A snowmobile, comprising: a frame; endless track for driving thesnowmobile; slide rails for mounting the endless track; at least onelinkage between the slide rails and frame, the linkage comprising apivot link, where the pivot link pivots in response to movement betweenthe slide rails and the frame; carrier rollers coupled to the at leastone linkage, with the endless track positioned over the carrier rollers;and at least one linear force element (LFE) positioned between thelinkage and the frame, whereby pivotal movement of the linkage strokesthe LFE.
 2. The snowmobile of claim 1, wherein the carrier rollers aresuspended by frame arms attached to the at least one linkage.
 3. Thesnowmobile of claim 1, wherein the at least one linkage furthercomprises a bell crank, which connects to one end of the LFE and to thepivot link.
 4. The snowmobile of claim 3, wherein the carrier rollersare suspended by frame arms attached to the bell crank.
 5. Thesnowmobile of claim 1, further comprising rear idler rollers coupled tothe slide rails, where the endless track extends over both the rearidler rollers and the carrier rollers.
 6. The snowmobile of claim 5,wherein the endless track extends at an angle of approximately 20-30° atsteady state.
 7. The snowmobile of claim 6, wherein the endless trackextends at an angle of approximately 24° at steady state.
 8. Thesnowmobile of claim 1, wherein the LFE is positioned above the carrierrollers.
 9. A snowmobile, comprising: a frame; endless track for drivingthe snowmobile; slide rails for mounting endless track; at least onelinkage between the slide rails and frame; carrier rollers coupled tothe at least one linkage, with the endless track positioned against thecarrier rollers; and at least one linear force element (LFE) positionedsubstantially horizontally, with one end attached to the frame and oneend connected to the at least one linkage.
 10. The snowmobile of claim9, wherein the at least LFE is positioned above the frame and thecarrier rollers.
 11. The snowmobile of claim 9, wherein the at least oneLFE is substantially horizontal throughout its movement.
 12. Thesnowmobile of claim 10, wherein the at least one linkage is comprised ofa pivot link attached to the slide rails.
 13. The snowmobile of claim12, further comprising a bell crank, pivotally mounted between the frameand the pivot link.
 14. The snowmobile of claim 13, wherein one end ofthe LFE connects to the bell crank.
 15. The snowmobile of claim 14,wherein the carrier rollers are suspended by frame arms attached to thebell crank.
 16. The snowmobile of claim 15, wherein the bell crank ispyramidally shaped, with front corners attached to the frame, rearcorners operatively coupled to the slide rails through the pivot link,and the apex attached to the LFE.
 17. The snowmobile of claim 9, furthercomprising rear idler rollers coupled to the slide rails, where theendless track extends over both the rear idler rollers and the carrierrollers.
 18. The snowmobile of claim 17, wherein the endless trackextends at an angle of approximately 20-30° at steady state.
 19. Thesnowmobile of claim 18, wherein the endless track extends at an angle ofapproximately 24° at steady state.
 20. A snowmobile, comprising: aframe; slide rails coupled to the frame; endless track mounted to theslide rails; at least one linear force element (LFE) positioned outsideof the envelope defined by the endless track; a suspension assemblycoupling the slide rails to the frame; carrier rollers coupled to thesuspension assembly; whereby one end of the LFE is attached to the frameand the opposite end is attached to the suspension assembly, with theendless track passing through the suspension assembly and over thecarrier rollers.
 21. The snowmobile suspension system of claim 20,wherein the suspension assembly comprises a linkage which pivots inresponse to movement between the slide rails and the frame, and the LFEis positioned between the linkage and the frame, whereby pivotalmovement of the linkage strokes the LFE.
 22. The snowmobile of claim 21,wherein the at least one linkage is comprised of a pivot link attachedto the slide rails.
 23. The snowmobile of claim 22, wherein the at leastone linkage further comprises a bell crank, pivotally mounted betweenthe frame and the pivot link.
 24. The snowmobile of claim 23, whereinone end of the LFE connects to the bell crank.
 25. The snowmobile ofclaim 24, wherein the bell crank is pyramidally shaped, with the carrierrollers coupled to the bell crank.
 26. The snowmobile of claim 25,wherein the carrier rollers are suspended by frame arms attached to thebell crank.
 27. The snowmobile of claim 26, further comprising rearidler rollers coupled to the slide rails, where the endless trackextends around both the rear idler rollers and the carrier rollers. 28.The snowmobile of claim 27, wherein the endless track extends at anangle of approximately 20-30° at steady state.